1. Field of the Invention
The present invention relates to control valves for controlling fluid flow in a tube, and more particularly, to an electromagnetic control valve in which a needle operable with an electromagnetic force is used for shutting off, or controlling fluid flow.
2. Background of the Related Art
In general, the control valve makes a linear control of an opening of an orifice for controlling a flow rate of a fluid flowing therethrough. In general, for making the linear control, a needle with a tapered tip is frequently used. In the valve, the needle is mounted such that the needle can make a linear reciprocating movement in a state the tapered tip of the needle is disposed opposite to one side of the orifice. When the needle makes the linear movement, an opened area of the orifice occupied by the tapered tip of the needle increases/decreases, according to which the flow rate of the fluid passing through the orifice can increase/decrease.
The valve for controlling a fluid flow according to the foregoing principle may have different structures for making the linear movement of the needle. A few related art structures used presently will be described.
As a related art exemplary control valve used up to now, there is a system in which a step motor is used as an actuator that moves the needle. In this case, there are a gear mounted on a rotation shaft of the step motor for converting a rotating motion into a linear motion, and the needle engaged with the gear. In this system, the needle moves in proportion to a number of pulses of a driving power provided to the step motor.
However, such a step motor system has disadvantage in that the valve cost is high due to the expensive step motor. Moreover, the requirement of hermetic sealing between the rotation shaft of the step motor and a valve body the needle is disposed therein causes difficulty in assembly of the valve, and a high production cost.
As another exemplary related art control valve used up to now, there is a system in which a diaphragm or a membrane is used. In this case, the needle is connected to the diaphragm or the membrane, and on a rear side of the diaphragm or the membrane to which the needle is connected, there is a separate space a pressure therein can be controlled by pressurizing the space with a fluid filled therein. This structure facilitates deformation of the diaphragm or the membrane by using expansion of the fluid caused by heating the fluid, according to which the needle can be moved.
However, this structure has disadvantages in that fabrication of a small sized valve is difficult due to the separate pressurizing space, and a great power consumption due to heat. Moreover, the structure has a low valve response speed as the valve is moved indirectly by using the expansion caused by heating of the pressurizing space.